This invention generally relates to aircraft braking systems and more particularly to a unique sensor configuration which provides electrical signals indicative of wheel brake reaction torque.
Typically, aircraft brake systems include a multidisk stack of stationary and rotating elements which, when interacting in an axial direction, effect a frictional engagement and impart braking action to the wheel. Engagement of the disk elements is provided by a plurality of axially positioned actuators, each actuator acting on an annular portion of a brake pressure plate. The actuators are moved simultaneously by a force supplied by hydraulic fluid pressure in the well-known and understood manner. Brake engagement, of course, is initiated by the pilot operating a foot actuated valve which applies hydraulic fluid pressure to the brake actuators.
Many aircraft, both commercial and military, also employ antiskid systems to the braking of the aircraft. These systems are primarily electronic and generally their operation involves sensing aircraft deceleration to provide signals to a pressure control valve so as to release brake pressure. Deceleration is detected by a transducer mounted in the wheel to sense wheel speed and provide electrical signals to the antiskid control circuitry. These antiskid systems operate in conjunction with presently used hydraulic braking systems through servo valves and valve driver circuitry which function to operate the brake actuators in the manner described above.
In addition to the above-mentioned systems, there is a requirement to limit brake reaction torque generated in the normal braking operation so as to permit optimum stress design of aircraft structural elements and in particular, the aircraft landing gear strut assemblies. Brake reaction torque is controlled by limiting the fluid pressure input to the brake actuators. One example of accomplishing this is described in U.S. Pat. No. 4,296,897 issued Oct. 27, 1981 and assigned to The Boeing Company. According to this disclosure, a "brake torque limiter" functions to reduce the input pressure to the wheel brake mechanism after a comparison is made between the brake reaction torque and the input pressure. If the brake reaction torque is greater than a predetermined amount which has been designed as a function of fluid pressure input, then the brake torque limiter reduces the pressure input to the brake mechanism accordingly.
Presently, there is also a desire by aircraft manufacturers to reduce aircraft weight and in so doing, gain a decrease in fuel consumption and/or provide increased payload capacity. One area which possesses distinct possibilities for such weight reduction includes the hydraulic system for wheel brake actuation. Obviously, any hydraulic system requires lengths of hydraulic hose or tubing, pressure control devices such as valves and the like, and a source of hydraulic fluid. Elimination of the hydraulic system therefore can result in substantial weight savings. In a copending application entitled "Electrically Actuated Aircraft Brake" I have disclosed various alternatives to the hydraulic actuators. These are specially configured electric motor actuators which drive the brake disk elements into engagement in response to an electrical input signal.
While the elimination of the hydraulic brake actuation system is a distinct possibility in view of the advancements being made inthe art, such elimination presents a need for an electrical torque sensing means since torque sensing is now accomplished by reason of its relationship to hydraulic pressure. This hydraulic pressure relationship, however, is not an actual reading of the torque reaction force but rather is a relative measure of the torque force. A sensor that reads the actual torque force therefore is required. Furthermore, it is considered that antiskid systems may use brake reaction torque in a feedback loop of the system electronics to enhance antiskid control. In this circumstance, an electrical signal indicative of actual brake reaction torque will be extremely useful, not only to an all electrical brake actuation system but also to an electronic antiskid control system.
Therefore, and in accordance with one aspect of the present invention, it is an object to provide a torque readout sensor that is electrical by design and is capable of reading the actual brake reaction torque of any aircraft wheel and brake configuration.
It is in accordance with another aspect of the invention an object to provide a torque readout sensor that is compatible with future "brake-by-wire" aircraft braking systems and which may also provide signals usable by electronic antiskid systems.
It is in accordance with still another aspect of the invention an object to provide a torque readout sensor that is simple by design, easily mounted on an aircraft wheel and brake assembly during factory assembly operations thereof, and which may be retro-fitted in the field to presently designed wheel and brake assemblies.
It is in accordance with a further aspect of the invention an object to provide a configuration for a torque readout sensor that may be temperature compensated and calibrated upon factory installation and/or may be retrofitted in the field and no further maintenance calibrations are required.